clk: exynos4: Fix wrong clock for Exynos4x12 ADC

The TSADC gate clock was used in Exynos4x12 DTSI for exynos-adc driver.
However TSADC is present only on Exynos4210 so on Trats2 board (with
Exynos4412 SoC) the exynos-adc driver could not be probed:
   ERROR: could not get clock /adc@126C0000:adc(0)
   exynos-adc 126c0000.adc: failed getting clock, err = -2
   exynos-adc: probe of 126c0000.adc failed with error -2

Instead on Exynos4x12 SoCs the main clock used by Analog to Digital
Converter is located in different register and it is named in datasheet
as PCLK_ADC. Regardless of the name the purpose of this PCLK_ADC clock
is the same as purpose of TSADC from Exynos4210.

The patch adds gate clock for Exynos4x12 using the proper register so
backward compatibility is preserved. This fixes the probe of exynos-adc
driver on Exynos4x12 boards and allows accessing sensors connected to it
on Trats2 board (ntc,ncp15wb473 AP and battery thermistors).

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Cc: <stable@vger.kernel.org>
Fixes: c63c5743 ("ARM: dts: Add ADC's dt data to read raw data for exynos4x12")
Reviewed-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Acked-by: Tomasz Figa <tomasz.figa@gmail.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>